AbstractSubclass is a class that provides additional services based on the services the potential super/parent class provides.

It is abstract in the sense that there are abstract requirements of what the super/parent class needs to implement.

See Also MixIn
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A simple example would be the EnumerableM''''''odule in RubyLanguage in which a class provides an InternalIterator method called 'each', then by including/mixing in the EnumerableM''''''odule, the original class will be enhanced with new functionalities such as collect, detect, find, includes, etc.